Abstract
Metal oxide dopants, such as titanium and chromium oxides, have garnered considerable attention for their potential to increase grain size (≥ 30 µm) in UO2 fuel, purportedly enhancing fission gas retention during reactor operation. Fuel performance is significantly impacted by fuel fracture behavior, so it is important to understand the effects of enhanced grain size and dopant content on UO2 fuel fracture. UO2 pellets were doped with 0.1 wt% TiO2 and 0.3 wt% Cr2O3 to alter density and grain size. Inductively coupled plasma mass spectroscopy measured dopant levels pre- and post-sintering. X-ray diffraction revealed lattice changes and microstrain via Rietveld refinement. Field emission scanning electron microscopy determined grain sizes of approximately 30 µm for TiO2 doping and 7 µm for Cr2O3 doping. Transverse rupture strength tests were performed on over 30 samples per dataset to obtain characteristic strength and Weibull modulus. Results indicate no statistical difference in fracture strength between 0.1 wt% TiO2 doped UO2 and undoped UO2, while 0.3 wt% Cr2O3 doped UO2 exhibited a 20% decrease in fracture strength. Doped UO2 samples also showed reduced Weibull modulus compared to undoped UO2, suggesting increased scatter in fracture strength. This study's findings suggest that titanium and chromium oxide doping in UO2, regardless of grain size, induce residual stresses, decreasing fracture strength and increasing variability in fracture behavior.
